Operating relay



Nov. 2 1926. 1,605,048

R. C. MATHES OPERATING RELAY hvenibr: Robe/'7 C. Mal/lest Patented Nov. 2 1926. I I

UNITED STATES I OFFICE.

ROBERT C. MATHES, OF WYOMING, NEW JERSEY, ASSIGNOR TO, WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF YORK.

oruna'rme RELAY.

Application filed m as, me. Serial No. ctacai.

This invention relates to relay operation rents is the greater depends only upon the and to repeating current waves, and has for direction of flow of energy in the line, so

an object to render a relay selectively rethat the resultant control action of the difsponsive to opposite directions of alternating ferentially acting currents upon the relay 5 current energy flow in a circuit, and to conmay readily be made to cause-the relay to be trol the pointing of a repeater in a line. selectively responsive to the direction of In accordance with the invention a relay energy flow in the line.

may be rendered selectively responsive to In the system of this invention the reactopposite directions of energy flow in a line ance network referred to above for connect- 1 by a network, preferably a network of reing the above mentioned biconjugate circuits actances connected to the line and controlling should preferably present to each of those the relay. circuits an impedance approximately equal In the form of the invention described to theimpedance of that one of those cirherein, the reactances of the network are cuits, so that the network will be a so-called 15 transformer windings, with four circuits maximum output network. Such networks taken therefrom, two of the circuits leading have been treated by Campbell and Foster 7 to the two line sections at opposite sides of in their article entitled Maximum output the relay, respectively, and the other two networks for telephone substations and recircuits taking off from the transformer peater circuits, published in the transacfill) windings two currents which are made to tions of the American Institute of Electrical control the relay difierentially. The trans- Engineers, 1920, Vol. 39, Part 1, pages 231 to former windings are preferably so related 290. that these four circuits are biconjugate when In an application of the invention to the they present the proper impedances to the reversal of the pointing of a telephone retransformer windings. For example, the peater, the relay made selectively responsive transformer windings may be related as in to the direction of energy flow in the line by any one of many well known types of soa network such as'is referred to above concalled hybrid coil connections employed for trols the reversal of the pointing of the reuniting a two-wire signalling circuit and its peater in the line, and preferably (in the artificial line with a four-wire signaling cirgeneral fashion disclosed in the application cuitin such manner as tolrender the twoof W. S. Gorton, Serial No. 635,865, May wire circuit and the artificial line conjugate 1, 1923, operating relays) the position of and to also render the input and the output the repeater in the line is so changed when branches of the four-wire circuit conjugate. the repeater is reversed that the network is 35 In such a two-wire to four-wire connection always on: the output side of the repeater so the two-wire circuit and the receiving branch that it can be reached by transmission apof the fourwire circuit (that is, the branch proaching the repeater from either line. which transmlits to the two-wire circuit) In the accompanying drawings Fig. 1 may be regarded as corresponding to the shows a circuit wherein a three-winding 40 two line sections at opposite sides of the retransformer is connected to a line and renlay to be selectively operated as mentioned ders a relay select vely responsive to oppo- 9 ab0ve, in the system of this invention; and site directions of alternating current energy the artificial line and the transmitting flow in the line; Fig. 2 shows an applicabranch of the two-wire to four-wire connection of the invention to the reversal of the tion may be regarded as corresponding to pointing of a telephone repeater; and Fig.

the remaining two circuits taken ofi from 3 shows diagrammatically the arrangement the reactance network, mentioned above, of of coils on transformers employed in the the system of this invention-that is, the two system of Fig. 2. circuits which take ofi from that network In Fig. 1, a hybrid coil 'll, having a balcurrents that are made to difierentially con-- ancing network Z and a bridge circuit Z, trol the relay which is to be selectively operconnects a line P to a line Q, for transmit- 0 ated in accordance with the direction of enting alternating currents, for instance teleergy flow in the line to which it is connectphonic currents, from each line to the ther. ed. Which of the difierentially active cur- The hybrid coil is shown as a three-winding equations consider the balanced repeating transformer with a winding or limb T in line P, a winding or limb T in line Q, and a winding or limb T in the circuit of the network Z The impedance of the balancing network Z includes the impedance of the input circuit of an amplifier rectifier 16, so that an electro-motive force across this impedance Z acts through the amplifier-rectifier 16 to cause direct current to flow in the lower winding of a polarized relay 15. The impedance of the bridge circuit Z includes the impedance of the input circuit of an amplifier-rectifier 14, and an electro-motive force across this impedance Z acts through the amplifier-rectifier 14 to cause direct our rent to flow in the upper winding of the polarized relay. These direct currents flow throu h the windings of the relay'in opposite dlrections with respect to the magnetic circuit of the relay. Thus the armature of the relay is drawn one way or the other depending upon the relative magnitudes of the energies. producing the electromotive' forces just mentioned. The amplifier-rectifiers are preferably electron tube devices, of the character described hereinafter in more detail in connection with Fig. 2.

It will now be shown that for energy flowing from line Q, todine P the energy due to the voltage E across impedance Z is greater than the energy due to the voltage E across impedanceZ and for energy flowing from line P to line Q the energy due to voltage E is greater than the energy due to voltage E For simplicity in working out the circuit coil to be made up with one to one windings each of total inductance 4L. Then each of the balanced windings will have an inductance L. The transformer will be con- Z 1 voltage drop across Z,

sidered to have no leakage, no iron losses and no D. C. resistance in its windings, but to be of finite inductance.

Let subscripts 1 denote impedance and Z 1; voltage drop across Z,

Now considering the case where a source of E. M. F. is inserted in line P, and using the same circuit constants and subscripts but small letters for the currents, we have,

From (12) and (13) -O=Z1'51 z z+ a w Combining this with (10) we get If windings T and T are equal, then with an E. M. F. inserted in line P no- I2- s 4) s' Whence 1 I,= ZZFEL 1,. 7

2+ 4 From (7) '2z,z +z z. 7 22.2. -z z. (a)

2Z3+Z2 Z2 Z1 2 or z z (14) And 2Z +Z Also ' i 2Z +Z i 2Z ,+Z (16) From (15) I supplies to the transformer dividing equally between the two impedances Z and Z under these conditions.

If windings T and T are equal, then with an E. M. F. inserted in line Q no current will flow through Z when Z equals Z multiplied by the impedance ratio of T to T theenergy which. the E. M, F. supplies to the transformer dividing equally between Z and Z, under these conditions.

It is not necessary to have an equal division of energy between Z and Z for transmission from ine P to line Q, or an equal division of energy between Z and Z, for transmission from line Q to to have the current in one of the windings of relay 15 zero in either case. For example, it in transmitting from line P to line Q it is desired to have three quarters of the voltage or the energy supplied by Z go to Z and only one quarter go to Z impedance Z may be made three times as great as Z and winding T may be given three times as many turns as windin T and if it is further desired, in transmitting from line Q to line P, to have three uarters of the energy or the voltage supp ied by Z go to Z and only one quarter go to Z impedance Z, multiplied by the impedance ratio of T to T, may be made three times as great as Z winding '1, being 'ven three times as many turns as windlng Thus, by proportioning the windings of the hybrid coil and the impedances "connected thereto, the ratio of the energies transmitted by the hybrid coil to the line and to the active winding of relay 15 may be varied, for each direction of transmission in lines line P, in order- Preferably, where winding T; and T are to have the same number of turns, the relation and combining with (16) we can get -4jpL (2Z +Z, "W +Z2) z' zl If we now assume that Z and Z are small compared to 2jpL (a condition met by well designed transformers) we get approximately Subtracting twice (12) .from (11) we get E,=Z i,2Z i,2Z,i,. (18) Substituting in 18) the values of i, and i Consider the line and network to be well balanced, that is, Z,-=Z =Z. Then equation (5) reduces to and (19) to- These are both of the same general form and may be differentiated for maximum power into impedances Z, and Z res ectively..

Power Taking the derivative of power with respect to Z we have On setting this expression equal tozero for maximum power and solving, we have oTreating the equation (21) in a similar manner and differentiating from maximum power, we obtain These two conditions taken together give us the relation When the network is designed for a maximum output network tomeet these ideal impedance conditions, that is,

it follows that the proper directionaloperfrom (17) and (14) in terms oft We get this 4 &

ation of the circuit will be maintained even if one of the balancing impedances is far from normal. For instance, equation 7A shows that if We have an infinite margin of operation. But it also follows that if Z, were so widely off of normal as to be zero or infinite the ratio of energies in Z to that in Z will be 2 to 1. Also if in equation 15A the impedance Z is made zero or infinite the ener in Z is twice the energy in Z and we Wlll have a safe margin of operation in the desired direction. Thus even if the outgoing line to which the repeater is connected has a very irregular impedance the circuit will function satisfactorily.

In Fig. 2 a repeater 17 comprising a repeating element 18, an input transformer 20 and potentiometer 21, and an output transformer 22, is reversibly connected to repeat from line Q to line P and from line P to line Q, the reversing being accomplished by a relay means or reversing switch 23. This reversing switch comprises four relays 24, 25, 26 and 27, which may be polar relays having armatures mechanically connected as indicated by bar 28.

The windings of each of the relays 24, 25, 26 and 27 of F ig. 2 are controlled in the same general manner as the windings of relay 15 of Fig. 1, but in Fig. 2 there is employed, instead of the transformer T of Fig. 1, a transformer arrangement X which comprises two three-winding transformers,

each of which has upon its core four coils which are wound in the same direction, as shown in Fig. 3. One terminal of each coil has been given an odd number and the other the next higher even number. The coils have been wound in such a direction that when current flows from an odd to an even terminal the flux set up in the core is in a given direction irrespective of which coil is taken. The same would be true if current were to flow from an even numbered to an odd numbered terminal, but in this case the flux would of course be in the opposite direction.

As stated, the transformer arrangement X consists of two transformers, each comprising four coils. The coils of these transformers are connected in groups A, B, C, and D,

, of two each, these groups being associated with the various circuits connected to the transformer arrangement. Thus the group A is connected with an impedance Z which corresponds to the impedance Z of Fig. 1, the group B is connected with an impedance Z which corresponds to the im edance Z of Fig. 1, the group C is connecte with an impedance Z correspondin to Z of Fig. the group D is connecte with an impedance 1 and.

Z corresponding to the impedance Z of Fig. 1. The coil 1-2 of roup A, together with the coils 34, 7-8 of group D and coil 5-6 of group B constitute one of the transformers of the transformer arrangement X, and in like manner coil 56 of group A, coils 34, 7-8 of group C and coil 12 of group B constitute the other transformer of the transformer arrangement. Since all of the groups are symmetrical, and the corresponding elements of each group have the same values, a balanced condition exists between the four circuits related to each other bythe said transformer arrangement. Let it be assumed that energy is being transmitted from impedance Z into the transformer arrangement X, and furthermore let the direction'of flow of current at any instant in group A be as indicated by the solid arrows. The current flowing in coil 1.2 of group A will induce a potential in the coils of group D that will cause flow of current from 4 to 7 and will also induce a potential in coil 65 of group B that will tend to cause a flow of current from 6 to 5. Similarly, the flow of current through coil 56 of group A, as indicated by the solid arrow, will induce a potential in the coils of group G that will cause flow of current from 4 to 7, and there will also be induced in coils 2-1 of group B a potential that will tend to cause current to flow in the direction indicated by the solid arrow. If the impedance Z, equal the impedance Z equal currents will exist in the coil groups D andC connected to these impedances, and as a result the potentials induced in the two coils of group B are equal inmagnitude. It will be seen, therefore, that no resultant current flows in the circuit of coil group B and impedance Z,. The current set up in group D will be transmitted in the direction of the arrows and will be fed into impedance Z,. The current set up in group C will be transmitted to the input circuit of the amplifierrectifier 14,- which corresponds to the amplifier-rectifier 14 of Fig. 1.

If, on the other hand, it is assumed that a signaling Wave is being transmitted fromimpedance Z into the transformer arrangement X, the distribution of energy in the said arrangement is as follows: The direction of flow of current of the transmitted wave in the group D is represented, for example, by the dotted arrows, viz., the current will flow through the coils of the said group in the direction from 7 to 4. This flow of current willinduce .potentials in groups A and B, which are related to group D by having one of their coils upon the same core. The potentials induced in coils 65 and 21 of groups A and B respectively will cause current to'flow in the directions indicated by the .dotted arrows. Since the circuits of groups A and B are neonate closed, current will flow in coils 2-1 and 65 of group A, and in coils 6-5 and 1-2 of group B in the directions indicated by the dotted arrows. If the impedance Z, equals the impedance Z, these currents will be of equal magnitude. in view of the fact that coils 12 and 6-5 of groups A and B respectively are upon the same magnetic core, and since the flow of current in coil 12 of group B is in opposite direction to the flow input circuit of an amplifier-rectifier 16 which corresponds to the amplifier-rectifier 16 of Fig. 1.

The amplifier-rectifier 16 comprises an amplifying tube 40 and an amplifying and rectifying tube 41. The amplifier-rectifier 14 comprises an ampli ing tube 43 and an amplifying and rectifying tube 44. The amplitier-rectifier 16 in Fig. 2 feeds the left-hand windings of each of the relays 24, 25, 26 and 27 through leads 45 and 46, just as the amplifier-rectifier 16 of Fig. 1 feeds the lower winding of relay 15 of Fig. 1; and the amplifier-rectifier 14 in Fig. 2 feeds the righthand windings of each of the relays 24, 25, 26 and 27 through leads 47 and 46, just as the amplifier-rectifier 14 of Fig. 1 feeds the upper winding of relay 15. In each of the relays 24, 25, 26 and 27, as in the relay 15,

the two windings of the relay act oppositely upon the magnetic circuit of the relay.

When the switch 23 is in the position shown, the relay 24 connects line Q to feed potentiometer 21, through the circuit from the upper end of the right-hand winding of a transformer t armature of relay 24,

leads 29 and 30, potentiometer 21, and loads 31 and 32 to the lower end of the righthand winding of transformer 29,. Also, with the switch 23 in the position shown, the relay 25 connects the output transformer 22 to feed line P through transformer arrange ment X, a transformer t contacts of relays 26 and 27, and a transformer t,,-the input circuit to transformer arrangement X being from the upper terminal of the secondary winding of transformer 22 through lead 34, armature of relay 25, lead 35, coil group A, and lead 32 to the lower'end of the secondary winding of transformer 22. The circuit through which the transformer arrangement X feeds transformer t extends from coil group D to the left-hand winding of transformer 2%,.

23 in the position The circuit through which transformer t, feeds transformer t extends from the upper terminal of the right-hand winding of transformer t through lead 36, armature of relay 26, lead" 37, armature of relay 27 to winding of transformer t, to

the lower end of the right-hand winding of transformer {5 When the reversing switch is operated, in 76 the manner described hereinafter, to the position alternative to that in which it has been shown, the line P is connected to feed potentiometer 21 through the transformer t the armature and right-hand contact of re- 80 lay 27 lead 30, potentiometer 21, and leads 31 and 32; and at the same time, the relay 26 connects the output transformer 22 to feed line Q, through transformer t the transformer arrangement X, contacts of lays 25 and 24, and transformer 16,. The circuit through which transformer 22 feeds transformer t extends from the upper end of the secondary winding of transformer 22,

through lead 34, armature of relay. 26., lead 0 36, right hand winding of transformer t and lead 32 to the lower endof the secondary winding of transformer 22. The circuit through which transformer 27, feeds the transformer arrangement X extends from the left-hand winding of transformer t, through the coil group D. The circuit through which the transformer t, extends from coil group A through lead 35, armature of relay 25, lead 24, and left-hand winding of transformer t back to coil group A.

It will be noted that switch 23 operates from to the alternate position, the pointing of the repeater between lines Q, and 'P, but also changes the position of the repeater 17 in the line, from its position between line Q, and transformer arrangement X to a position between line P former arrangement 'X..' Similarly, when the reversing switch 23 operates to the position in which it is'shown, the repeater is shifted from a position between line P and when the reversing the position shown transformer arrangement X to a connection between line Q3 and transformer arrange.- ment X.

The operation of the system shown in Fig. 2 will now be apparent, With switch shown, the system is for repeating from line Q to line P, the input and output circuits of the repeater being as traced above. The system remains in this condition until transmission approaches the repeater output over line energy approaches the input of the repeater over line Q and is amplified and transmitted to line P, the voltage applied to Z will be greater than that applied to Z as explained ahove,- eo that coil group G the upper end of' 7a the left-hand winding of transformer t,, I and from the lower end of the left-hand 38, armature of relay me it not only reverses 105 and trans- 1 set P; for when will cause amplifier-rectifier 14 to feed to the right-hand winding of each of relays 24, 25, 26 and 27 a current greater than that which coil group B causes amplifier-rectifier 16 to feed to the left-hand winding of each of the relays 24, 25, 26 and 27.

When transmission approaches the repeater output from line P, the switch 23 eing in the position shown, transformer t, supplies current to transformer :5 through the armatures of switches 27 and 26, and the transformer t delivers energy to coil group lines having the D of transformer arrangement X. Therefore the voltage applied to Z will be greater than that applied to Z as'explained above, so that coil grou -B will cause am lifierrectifier 16 to fee to the left-hand winding of each of relays 24, 25, 26, and 27 a current greater than that which coil oup G causes amplifier-rectifier 14 to feef to the righthand winding of each of the relays 24, 25, 26 and 27. These switching relays therefore reverse, causing the ointing of the repeater to be reversed an the position of the repeater in the line to be changed as ereplained above. The direction of flow of the transmission through the transformer arrangement X is the same after the accomplishment of the reversal of the repeater as when the reversal of the repeater was initiated; and therefore the amplified transmission from line P to line Q tends to hold the repeater pointed toward line Q. The repeater remains pointed toward line Q until transmission approaches its output from line whereupon the pointing of the repeater and the position of'the repeater in the line are again changed. As a result of the changing of the position of the repeater in the line at each reversal of the repeater, the transformer arrangement X is always vin the line at the output side of the repeater so that it can be reached by transmission approaching the repeater from either line.

For a given adjustment the means shown in Fig. 2 for rendering the rela devices selectively responsive to opposite irections of energy flow in the lines will operate best when employed on lines having impedances within certain limits, as in the case of the corresponding means of Fig. 1. y In Fig. 2, as wasnoted in connection with Fig. 1, for

roper impedance the current in one of t e impedances Z and Z,, is zero and the current in the other one of these two impedances has a finite magnitude, these two impedances and the two lines P and Q constituting a biconjugate network, with the impedance Z conjugate to one of the lines, and the impedance Z, conjugate to the other line. As indicated above, the impedance relations between these four arts of the bicQnjugJate network, of either .1 or Fig. 2 may e regarded as corresponding to those between the line, balancing network,

repeater output branch and repeater input branch of the maximum output hybrid coil connection commonly employed in 22-type repeaters such as described in an article by Gherardi, and Jewett published in the Transactions of the American Institute of Electrical Engineers for 1919, Vol. XXXVIII, Part II, page 1287. In such a hybrid coil connection the line and the repeater output branch may be regarded as corresponding to the two line sections of the repeater circuit of this invention, and the balancing network and the repeater input branch of the 22-type repeater circuit may be regarded as corresponding to the impedances of the input circuits of the amplifierrectifiers of the circuit of this invention. In the circuits of this invention, the network connecting the two line sections and the input circuits of the amplifier-rectifiers should preferably resent to each one of said line sections and input circuits an impedance approximately equal to the impedance of each such one of the two line sections or input circuits, so that the network will be a maximum output network. However, the means of Fig. 2 for rendering the relay devices selectively responsive to oppositely directed transmission will work directionally regardless of the impedances of the lines into which it works, as was the case with the correspondin means of Fig. 1.

It shou d be understood that the invention is capable of embodiment in forms and arrangements other than those shown, without departing from the spirit and scope of the appended claims.

The invention claimed is:

1. The. combination with a two-way transmission circuit comprising two sections, of a relay, two circuits for controlling said relay, and means comprising a plurality of coupled reactances for associating said sections with, each other and with said relay controlling circuits, said reactances being proportioned with respect to the impedances of said sections and said relay controlling circuits so that ener transmitted over said transmission circult in one direction will control said relay in one sense and energy transmitted over said transmission circuit in the opposite direction will control said relay in another sense.

2. A circuit for transmitting alternating current energy in opposite directions, a relay havin an armature, and means whereby said re ay is caused to operate its armature in o posite directions in accordance with the direction of transmission of the alternating current ener in said circuit, said means comprising a t ee winding transformer having two of its windings in said circuit and having its third winding in mductive relation with said relay,

8. A two-way transzmssion circult, a poenergies against larized relay having an armature and windings, and means whereby said relay is caused to operate its armature in opposite directions in. accordance with the direction of transmission in said circuit, said means comprising a three-winding transformer, connected to said circuit and to said relay windings.

4. A circuit for transmitting alternating currentcnergy in opposite directions, a relay armature, and means foroperating said armature in opposite directions in accord ance with said. opposite directions of said energy transmission in said circuit, said means comprising means for deriving alternating current energies from diifer ent parts of said circuit, combining said derived energies and controlling said relay armature in accordance with the resultant efiect, said last mentioned means comprising a threewinding transformer connected to said circuit.

5. A circuitfor transmitting alternating current energy in opposite directions, a uni directional current transmitting device connected therein, means comprising a relay armature for controlling the transmitting emciency of said device in a given direction, and means for operating said armature in opposite directions in accordance with said opposite directions of said energy How in said circuit, said second mentioned means comprising means for deriving alternating current energies from different parts of said circuit, balancing said derived energies against each other and controlling said relay armature in accordance with the-resultant efiect, and said'last mentioned means comprising a three-winding transformer connected to said circuit.

6. A. circuit for transmitting alternating current energy in opposite directions, a unidirectional current transmitting device connected therein, means comprising a, relay armature for controlling the transmitting efficiency of said device in a given direction, and means for operating said armature in opposite directions in accordance with said opposite directions of said energy flow in said circuit, said second mentioned means comprising stationary means for deriving alternating current energies from diiierent parts of said circuit, balancing said derived each other and controlling said relay armature in accordance with the resultant eifect, and said last mentioned means comprising a three-winding transformer connected to said circuit.

7. A circuit for transmitting alternaing current energy in opposite directions, a unidirectional current transmitting device, switching means for connecting said device to' said circuit, means comprising a relay armature for controlling said switching means, and means for operating said armature in cuit is greater than the taken ratio of winding transformer which opposite directions in accordance with said opposite directions ofthe energy transmission in said circuit, said third mentioned means comprising means for deriving alternating current energies of said circuit, combining said derived energies and controlling said relay armature in accordance with the resultant effect, and

said last mentioned means comprising a. three-wlnding transformer connected to said circuit.

from different parts 8. A line, a unidirectional current transmitting device connected therein, means for dlstingulshlng between opposite directions of electrical energy transmission in said line,

and means controlled by said'first-mentioned means for controlling the pointing of said device, said first-mentioned means comprising a three-winding transformer connected to said line and to said second mentioned means. 7

9. A line for transmitting alternating current energy in opposite directions, a repeater adapted to be connected therein, a relay coniprismg an armature, stationary means-for causing said relay to tend to operate its armature in opposite directions in accordrent energy transmission in said line, and means controlled by said relay for controlling the connection of. said repeater in said line, said stationary winding transformer connected to said line and also including means connecting said three-winding transformer to said relay.

10. In combination, a circuit, twoimpedances, means comprising a three-winding transformer so connecting said impedances to said circuit that the ratio of the electromotive forces across said impedances due to one direction of energy flow in said circorrespondingly the electromotive forces across said impedances due to the opposite direction of energy flow in said circuit, and two differentially acting relay windings connected across said two impedanccs, respectively.

11. In combination, a circuit, a switch deance with the direction of alternating curvice, and means for rendering said switch device selectively responsive rections of energy means comprising a network having branches conjugate respectively to two parts of said circuit, and said network comprising a threehastwo of its windings connected in said two parts, respectively, of said circuit and has its third winding connected in circuit with one of said branches.

12. In combination, a. line comprising two sections, a relay device, and means for rendering said device selectively responsive to opposite directions of energy flow in said line, said means comprising two impedances and a network so coecting said two imto opposite dimeans including a three-.

flow in said circuit, said.

Inn

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pedances and said two line sections as to present to each of said line sections and impedances an impedance approximately equal to the impedance of that one of, said two line sections or said two impedances, and said network comprising a three-winding transformer having two of its windings in circuit with said two line sections, respectvely, and having its third Winding in circuit with one of said two impedances.

13. In combination with a line having two sections, a directional circuit, said directional circuit comprising two relay circuits and transformer windings for connecting one of said relay circuits substantially in conjugate relation with one of said line sections, and the other of said relay circuits substantially in conjugate relation with the other of said line sections, and differential means controlled by said relay circuits.

14. In combination with a line having two sections, a directional circuit, said directional circuit comprising two relay circuits and two three-winding transformers for connecting one of said relay circuits substantially in conjugate relation to one of said line sections and the other of said relay circuits substantially in conjugate relation to the other (if said line sections, and difierential means controlled by said relay circuits.

In witness whereof, I hereunto subscribe my name this 19th day of July A. D., 1923.

ROBERT C. MATHES. 

